The Protein Arginine Deiminases (PADs) are a family of enzymes that catalyze the post-translational conversion of peptidyl-arginine to peptidyl-citrulline, a process more commonly referred to as deimination or citrullination (Jones, J. E., Causey, C. P., Knuckley, B., Slack-Noyes, J. L., and Thompson, P. R. (2009), Curr Opin Drug Discov Devel 12, 616-627; Vossenaar, E. R., et al. (2003), Bioessays 25, 1106-1118). There are five PAD isozymes in humans and other mammals (which are denoted PADs 1, 2, 3, 4, and 6), and the activity of multiple family members is aberrantly increased in different diseases, including rheumatoid arthritis (RA), Alzheimer's disease (AD), multiple sclerosis (MS), lupus, Parkinson's disease, and cancer. For example, increased PAD levels are observed in synovial fluid (RA) (Kinloch, A., et al. (2008), Arthritis Rheum. 58, 2287-2295) during NET formation (colitis and lupus) (Wang, Y., et al. (2009), J. Cell. Biol. 184, 205-213), within the brains of patients with MS (Wood, D. D., et al. (2008), Lab. Invest. 88, 354-364), in the joints of patients with osteoarthritis (Kinlock A., et al. (2008), in ulcerative colitis lesions (Chen, C. C., et al. (2008), Clin. Immunol. 126, 165-171), in the hippocampal extracts of AD patients (Ishigami, A., et al. (2005), J. Neurosci. Res. 80, 120-128), and in several types of carcinomas (Chang X., et al. (2009), BMC Cancer 9, 40). Furthermore, the administration of Cl-amidine, a potent PAD inhibitor (Luo, Y., et al. (2006), Biochemistry 45, 11727-11736), has proven useful in decreasing disease severity in animal models of ulcerative colitis and RA (Chumanevich, A. A., et al. (2011), American Journal of Physiology—Gastrointestinal and Liver Physiology 300, G929-G938; Willis, V. C., et al. (2011) J. Immunol. 186, 4396-4404).